Islet Tissue Macrophages in Immunity Homeostasis and Type 1 Diabetes

Islet macrophages are considered to be irreplaceable in maintaining the immune microenvironment homeostasis. The M1/M2 imbalance can trigger the initiation of islet autoimmunity and persists throughout the entire process of type 1 diabetes. The identification of macrophage transcriptional clusters and phenotypes by single-cell sequencing has facilitated in-depth studies on the role of macrophages in the pathogenesis of type 1 diabetes. Macrophages exert extensive endocrine and paracrine effects on the islets by secreting various bioactive chemicals, especially exosomes, which facilitate cell-cell communication. Resident islet macrophages directly influence the biological properties of islet tissue. Meanwhile, the interaction between macrophages and islet cells is bidirectional. Cell-cell interactions also closely govern the polarization and activity of macrophages. An imbalance in the transition from M2 to M1 macrophages may lead to inflammation and islet dysfunction. Here, we have discussed the latest research progress on macrophages in the islet immune microenvironment homeostasis, the mechanisms of interactions between macrophages and islet cells in type 1 diabetes, and analyzed the possible clinical consequences. Furthermore, we highlighted emerging technologies for non-invasive detection of macrophages and summarized how therapeutic targeting of macrophages may be beneficial for patients with type 1 diabetes.